This invention relates to a selvage forming system of a shuttleless loom, more particularly to an improvement in a selvage forming system of the shuttleless loom of the type wherein rigid selvage structures are formed at both sides of a woven fabric by binding cut end portions of weft yarns with binding yarns.
It is well known that a shuttleless loom is equipped with a selvage forming system which forms selvage structures at the both sides of a fabric during weaving operation of the fabric. The selvage structure is necessary for preventing warp yarns to fray or separate from the both sides of the woven fabric. It is also well known that two binding yarns or threads are twisted together, putting the ends of picked weft yarns between the two binding yarns. In such a selvage forming system, two binding devices, in general, are installed adjacent the both sides of the array of the warp yarns and located opposite to each other. The two binding yarns are drawn from each binding device and guided to the one side of the array of the warp yarns. Then, the two binding yarns continue alternately their opening and closing actions generally at the same time respectively as the opening and closing actions of the array of the warp yarns. Simultaneous, the two binding yarns are twisted together at each pick of the weft yarn to the shed of the warp yarn, to put the ends of the picked weft yarn between the two binding yarns. As will be appreciated from the foregoing, the essential part of each binding device is composed of a rotatable mechanism.
The two binding devices are usually driven to rotate their rotatable mechanisms by a drive shaft for rotatably connecting them. Accordingly, the rotatable mechanisms of the two binding devices are rotated in the same direction with respect to the shuttleless loom. However, the mechanisms are rotated in opposite directions to each other with respect to each binding device itself. Hence, two binding yarns from one binding device are twisted in the direction opposite to that in the two binding yarns from the other binding device.
Now, when a fabric is woven with so-called "spun yarns," it is necessary to use the same spun yarns as the binding yarns for forming the selvage structures of the woven fabric. Because, if so-called "filament yarns" are used as the binding yarns for spun yarn fabric, shrinkages may occur at the selvage structures of the fabric, which are caused by the fact that the shrinking characteristics between the spun yarn and the filament yarn are considerably different.
In case of using a two-ply cotton yarn as each binding yarn, assuming that the weft yarn density is 31 yarns per cm, the two binding yarns are twisted 1550 times per meter of the woven fabric. With respect to the two-ply cotton yarn, about 1000 times twistings per meter are applied to it. Therefore, if the two binding yarns are twisted, during selvage formation, in the direction opposite to that of the twistings previously applied to the two-ply cotton yarn, the twistings previously applied to the two-ply cotton yarn may be almost cancelled. This considerably lowers the strength of the binding yarns for forming one of the two selvage structures of the fabric and therefore the binding yarns of the one selvage structure are liable to cut. Hence, the one selvage structure is also liable to easily break. In order to prevent such a selvage structure breaking, it will be considered to use specially prepared two-ply yarns which are previously twisted in the direction opposite to that in usual two-ply yarns, as the binding yarns for forming the one selvage structure. However, this causes the management of weaving to be troublesome. Furthermore, if such two kinds of binding yarns are used in error, the twistings of all the binding yarns will be cancelled.